In a conventional shift range switcher, a shift range switching operation performed by a driver to switch a shift range is detected by using a switch or the like, and a motor is driven in accordance with a detection signal of the switch so that the shift range can be switched.
When the driver turns ON an ignition switch, the shift range switcher performs an initial learning process for learning a relationship between a rotation position of the motor and an output signal of an encoder that detects the rotation position of the motor.
In a shift range switcher disclosed in US 2011/0175563 corresponding to JP-A-2011-151931, when the initial learning process is performed once, the initial learning process is prohibited for a predetermined period of time that allows the motor to be cooled to a predetermined temperature. Thus, even when the driver repeatedly turns ON and OFF the ignition switch, a significant increase in temperatures of the motor and an electronic controller for energizing the motor are prevented so that the motor and the electronic controller can be protected from heat damage.
In a shift range switcher disclosed in US 2008/0024081 corresponding to JP-A-2008-32176, when the driver performs the shift range switching operation at a short interval that cannot suitably cool the motor, the number of times the shift range switching operation is performed at the short interval is counted. Then, when the counted number reaches a predetermined number corresponding to allowable temperature limits of the motor and the electronic controller, the electronic controller is prohibited from energizing the motor for a predetermined period of time. Thus, a significant increase in temperatures of the motor and the electronic controller is prevented.
One disadvantage of the shift range switcher disclosed in US 2011/0175563 is that when the initial learning process is performed once, the initial learning process is always prohibited for the predetermined period of time.
One disadvantage of the shift range switcher disclosed in US 2008/0024081 is that the temperature of the motor is estimated based on only the number of times the shift range switching operation is performed. That is, the temperature of the motor is estimated without consideration of the fact that the motor is cooled at a little within the short time interval. Therefore, the electronic controller may be prohibited from energizing the motor unnecessarily. Further, another disadvantage of the shift range switcher disclosed in US 2008/0024081 is that when the counted number reaches the predetermined number, the electronic controller is always prohibited from energizing the motor.